1. Field of the Invention
The present invention relates generally to a recording medium for use in recording/reproducing audio information, video information or ordinary data, and more particularly to an optical disk structure capable of recording/reproducing signals by means of light, a method of manufacturing the optical disk structure and an apparatus for manufacturing the optical disk structure.
2. Description of the Related Art
There is known an optical disk constructed so that recorded signals are reproduced by means of a laser beam. In an example of this type of optical disk, signal recording areas are provided on both sides of the disk.
Recently, a small-sized video disk (with a diameter of about 12 cm) for high-density recording has been developed. In the small-sized, high-density video disk, most of a flat portion of the disk extending from a central hole to a recording start region is used as a clamp zone (to be clamped and held by a disk holding mechanism). Thus, the flat portion functions as a reference surface of the disk in relation to the optical system when the disk is mounted on a turntable and clamped by a clamper.
If a conventional label is attached to this disk as an indication label, the following problems (a) and (b) will occur:
a) Because tilt (inclination) tolerance angle of the disk is to be very small, even if the disk is slightly inclined, the quality of a reproduced signal is greatly degraded. If the above-mentioned indication means is used, the disk tends to be easily inclined due to a sheet attached to the clamp zone or unevenness of printed ink, etc. PA1 b) A sheet is attached, or ink, etc. is printed, on a limited area of the clamp zone of the disk. When the disk is mounted on the turntable and held by the clamper, the clamper may cause damage to the indication surface due to a slip which occurs, in particular, at the time of start of the operation. As a result, the indication may become unclear, the reference surface of the clamp zone may be inclined, or the indication label may be removed. PA1 an inner surface of a portion of at least one of the light transmissive disk substrates, the portion facing a clamper and being located around the central hole; PA1 an indication label provided on the inner surface by means of one of printing and attachment; and PA1 the adhesive layer with light shielding properties, provided between the indication label and the other of the light transmissive disk substrates. PA1 a recess portion recessed in a thickness direction in a portion of at least one of the light transmissive disk substrates around the central hole; and PA1 an indication label provided on a bottom surface of the recess portion by means of one of printing and attachment.